Fatigue Behavior of Dissimilar 5754/7075 and 7075/5754 Spot Friction Welds in Lap-Shear Specimens

Fatigue behavior of spot friction welds or friction stir spot welds in lap-shear specimens of dissimilar aluminum 5754-O and 7075-T6 sheets is investigated based on experimental observations and two fatigue life estimation models. Optical micrographs of the 5754/7075 and 7075/5754 welds after failure under cyclic loading conditions are examined to understand the failure mechanisms of the welds. The micrographs show that the 5754/7075 welds mainly fail from the kinked fatigue crack through the lower sheet thickness. Also, the micrographs show that the 7075/5754 welds mainly fail from the kinked fatigue crack through the lower sheet thickness and from the fracture surface through the upper sheet thickness. A kinked fatigue crack growth model based on the stress intensity factor solutions for finite kinked cracks and a structural stress model based on the closed-form structural stress solutions are adopted to estimate the fatigue lives of the 5754/7075 and 7075/5754 welds in lap-shear specimens. The fatigue life estimations based on the kinked fatigue crack growth model and the structural stress model agree well with the experimental results.